Recovery of chlorinated methanes



United States Patent 3,148,041 RECOVERY OF CHLORINATED METHANESFrederick Chris Dehn and Robert E. Feathers, New Martinsville, W. Va,assignors to Pittsburgh Plate Glass Company, Pittsburgh, Pa, acorporation of Pennsylvania No Drawing. Continuation of application Ser.Ne. 812,578, May 12, M59. This application Nov. 21, 1951, Ser. No.154,062

11 Claims. (Cl. 55-61) The present invention relates to a method ofrecovering chlorinated methanes. More particularly, the presentinvention relates to the recovery of chlorinated methanes from gasmixtures produced by the oxychlorination of methane.

It has been proposed to chlorinate lower aliphatic hydrocarbons such asmethane, utilizing gaseous hydrogen chloride as the chlorinating agent.In processes of this type, gaseous hydrogen chloride and an oxygencontaining gas such as air, and the hydrocarbon to be chlorinated arepassed in contact with ametal halide catalyst. By a series of well knownreactions, elemental chlorine (C1 is released from the hydrogen chlorideand chlorinates the hydrocarbon feed material. In another modificationof this process, elemental chlorine (C1 is used as the feed gas in placeof gaseous HCl. This latter process operates in a manner similar to thefirst except that an initial chlorination of hydrocarbon takes place.Thus, free chlorine, an oxygen containing gas, and the hydrocarbon to bechlorinated are passed in contact with a metal halide catalyst. Thechlorine reacts with the hydrocarbon to produce hydrogen chloride and achlorinated product of the hydrocarbon. Hydrogen chloride produced inthis manner is then converted to elemental chlorine by a well knownseries of reactions, thereby providing additional chlorine for thechlorination of more hydrocarbon feed.

Although chlorinations of this type are well known in the art, there areserious operational diificulties generally associated with them. Thus,for example, it is found that serious difiiculty arises in the recoveryof the chlorinated hydrocarbon products issuing from such reactions.This is due in part to the fact that the chlorinated hydrocarbonproducts are diluted in great quantities of inert or noncondensiblegases such as elemental nitrogen, carbon monoxide, carbon dioxide, andother like gases. In order to recover the products satisfactorily fromsuch a process, therefore, it is necessary to process great quantitiesof gas and efliciently recover the chlorinated hydrocarbon contentthereof.

According to the present invention, it has been found that by contactinggas mixtures containing chlorinated methanes and predominatingquantities of noncondensible gaseous components with a liquid aromatichalogenated hydrocarbon, that it is possible to absorb essentially allof the chlorinated methane content of such a mixture while permittingthe non-chlorinated methane constituents of the gas mixture to passthrough the absorbent. Recovery of the absorbed chlorinated methanesfrom the liquid aromatic halogenated hydrocarbon can conveniently beaccomplished by simple distillation techniques. In addition toefliciently recovering the chlorinated meth ane content of apredominantly noncondensible gas stream, it is found that little or noliquid aromatic halogenated hydrocarbon absorbing material is swept outof the contact area during the absorption. The process lends itself tooperations which are conducted either on a continuous basis or asbatchatype operations.

Typical compounds contemplated are halogenated diphenyls such as2-brornodiphenyl, 2-chlorodiphenyl; halogenated naphthalenes such asl-bromonaphthalene, 1- chloronaphthalene, 1,2-dichloronaphthalene;halobenzenes 3,l48,h4l Patented Sept. 8, 1964 and mixtures thereof. Thecontemplated aromatic halogenated hydrocarbon and mixtures thereofnormally are liquid at 25 C. and atmospheric pressure. In all events,they include compounds having melting points below 50 to C. and boilingpoints above C. at atmospheric pressure (760 millimeters of mercury).Liquid halobenzenes form a preferred solvent in the herein disclosedprocess.

The term halobenzenes as used herein in the specification and claims indescribing the absorbing medium, is intended to include halogensubstituted benzenes having the physical characteristics referred toabove. The halogen substituted benzenes may contain one or more halogenson the ring and they may be mixed halogens or a single species. Inaddition to the presence of halogen substitutions, substitutedfunctional groups may also be present on the ring. Thus, hydroxyl,nitro, alkyl, and other like groups may be substituted on the ring inaddition to the halogen present.

Typical of some of the halobenzene absorbing materials contemplated foruse in the present invention, are 1,2-dichlorobenzene;1,3-dichlorobenzene; 1,4-dichlorobenzene; chlorobenzene;l-chloro-2-nitrobenzene; 1-cbloro-3-nitrobenzene; bromobenzene;l-bromo-3-chlorobenzene; l-bromo-4-chlorobenzene; l-bromo-Z-iodobenzene;1-bromo-2-nitrobenzene; 1,2-dibromobenzene; 1,3-dibromobenzene;1,2,3,4-tetrachlorobenzene; 1,2,3,5-tetrachlorobenzene;1,3,5trichlorobenzene; l-chloro-2,4-dinitrobenzene;4-chloro-1,2-dinitrobenzene; 1-chloro-4-fluorobenzene;l-chloro-2-hydroxybenzene; 1-chloro-3-hydroxybenzene;1-ch1oro-4-hydroxybenzene; 2,3-dichlorophenol; 2,4-dichlorophenol;2,5-dichlorophenol; 2,6-dichlorophen01; 3,4-dichlorophenol;3,5-dichlorophenol; 2-chloro-1- methylbenzene; 3-chloro-l-methylbenzene;4-chloro-1- methylbenzene; 4,6-dibromo-1,3-dimethylbenzene; 1,2,4-trichlorobenzene; o-xylyl bromide; 4-brorno-o-xylene; o-xylyl chloride;o-xylylene chloride, and other like compounds. Mixtures of halobenzenesmay also be employed provided the mixture employed exhibits the meltingpoint and boiling point characteristics hereinabove set forth.Orthodichlorobenzene forms a preferred solvent for the absorption ofchlorinated methanes.

Gas streams containing predominating quantities of inert ornoncondensible gases with low concentrations ranging below 25 percent byvolume of chlorinated methanes, are produced during the oxychlorinationof methane in the presence of a catalyst, utilizing either HCl orelemental chlorine (C1 as the chlorinating agent together with oxygen.Processes of this type are conducted in the presence of a metal halidecatalyst and usually in tubular reactors, though other type reactors maybe employed.

The metal used in the catalyst is one of variable valence such ascopper, chromium, iron and the like, and may be employed alone or incombination with other metals such as sodium, potassium and the like.Preferably, catalysts are in the form of metal chloride salts and areimpregnated on an inert material which provides considerable surfacearea for the process reactants to contact the catalyst. Various carriersmay be employed such as, for example, silica gel, alumina, kieselguhr,pumice and other well known carrier materials. A particularly suitablematerial is Celite, a calcined diatomaceous earth (Lompoc, California,diatomite) manufactured by the lohns-Manville Corporation. This materialimpregnated with a cupric chloride-potassium chloride catalyst, has beenfound particularly desirable in conducting oxychlorination reactions ofthe type which produce gas mixtures containing low chlorinated methanevolume concentrations.

A free elemental oxygen containing gas is employed as one of the feedmaterials in these reactions. Thus,

elemental oxygen is found suitable for use in the process and may beemployed alone or mixed with various inert diluents such as nitrogen,argon, neon and the like. Air comprises a particularly suitable gas forsupplying elemental oxygen to the process since it is easily obtainedand inexpensive. Other types of oxygen containing gases, that is, gaseswhich contain elemental oxygen therein, may also be employed. Thus,oxygen enriched air, oxygen or air mixed with inert gases, or vapors ormixtures of oxygen, air and inert gases or vapors may be convenientlyutilized in accordance with the teachings of the present inventionwithout impairing the results in any way.

Generally, temperature and pressure conditions utilized in anoxychlorination reaction may be varied considerably without seriouslyinterfering with the process. While it is preferred to operate thesystem at or near atmospheric pressures for operational convenience,both superatmospheric pressures and subatmospheric pressures may beutilized if desired. Similirly, temperatures between 45 0 C. to about550 C. are preferably employed in the catalyst zones contained in thereactors. Considerable variations in these temperatures may be made,however, without detrimental effect, thus temperatures may be lowered to350 C. or lower, or raised to 700 C. or higher, if desired.

The feed ratios of the various components of the feed gases reacted inthe catalyst zones may be subjected to considerable variation withoutseriously interfering with the process. Thus, for example, thechlorinating agent employed may be fed to the system at a rate such thatfrom between 0.5 mole to about 5 moles, or even more, chlorinating agentis supplied for each mole of the hydrocarbon fed. Less than 0.5 mole ofchlorinating agent may be utilized for each mole of hydrocarbon fed inthe process of this invention, but will usually result in supplying toosmall a quantity of chlorine to completely chlorinate all of thehydrocarbon fed. Employment of a chlorinating agent in excess of 5 molesfor each mole of hydrocarbon, is likewise permissible though chlorinewill be supplied in quantities greater than necessary to completelychlorinate all of the hydrocarbon fed.

Oxygen is supplied to insure the complete oxidation of the chlorinatingmedium. Considerable amounts of eX cess oxygen may be employed ifdesired, but quantities supplying more than 5 percent by volume freeoxygen in the exit gas stream are not particularly beneficial. Oxygencontent of the feed gases is therefore preferably maintained so thatbetween about 0.8 mole and 1.5 moles of free oxygen are supplied to thesystem for each mole of chlorinating agent. The hydrocarbon feedmaterial may comprise preferably methane, but natural gas or any othergaseous mixture containing predominating quantities of methane may beemployed as hydrocarbon feed material.

Gas mixtures containing small volumes of chlorinated methanes in largequantities of inert gas are conveniently produced by charging a jacketedtubular reactor throughout a substantial portion of its length, with ametal halide catalyst impregiated on an inert carrier material. Thereactor is regulated in temperature by circulating a molten salt mixtureor other suitable heat transfer material in the jacket of the reactor. Amixture of the methane to be chlorinated, an oxygen containing gas and achlorinating agent selected from the group consisting of HCl, C1 or amixture of HCl and C1 are fed into the reactor at one end. The gaseousreactant products are removed at the end of the reactor opposite thefeed inlet and either continuously or at periodic intervals of time, areintroduced into an absorbing zone and contacted with the liquid aromatichalogenated hydrocarbon solvent. Contact of the gaseous mixture with theliquid aromatic halogenated hydrocarbon results in the absorption of thechlorinated methane content of the gas stream while permittingsubstantially all of the inert gaseous com- 4 ponents of the mixture topass through the solvent unaffected. The liquid absorbent is found quitestable and little or no loss of absorbent occurs despite the largequantities of gases passing in contact with it.

Absorption techniques contemplated for use in recovering chlorinatedmethanes from gas mixtures in accordance with the teachings herein setforth, include both pressure absorption systems and absorption systemsoperated under substantially atmospheric conditions. Packed, unpacked,bubble cap, perforated plate and other similar type columns are typicalof equipment which is conveniently utilized to conduct the absorption ofchlorinated methanes. Packed columns typically contain beryl saddles,Raschig rings or other suitable packing material. As a preferred mode ofoperation, packed columns containing beryl saddles are employed.Conventional structural materials, preferably corrosion resistant suchas steel, nickel, glass and alloys lined or unlined, are utilized inconstructing the columns utilized herein.

The ratio of the feeds to the absorption zones is considerably variableand will depend upon the efficiency of the column employed. Generally,low ratios of liquid to gas are desirable since they reduce considerablyequipment requirements for handling large quantities of liquid. Thus,molar ratios of between 1 and 15 are usually satisfactory andpreferably, ratios between 1 and 10 are employed. Ratios lower than theabove ranges, if capable, are desirable.

Column temperatures may vary somewhat, though it is preferable tooperate the system at the lowest possible temperature compatible withthe physical properties of the absorbent utilized. Ambient temperatures(25 C.) where permissible are preferred.

Desorption of the chlorinated methanes from the liquid aromatichalogenated hydrocarbon in accordance with this invention, is preferablyaccomplished by recourse to steam stripping techniques. Strippingcolumns employed may be packed, unpacked, bubble cap, perforated plate,and the like. Facked columns form a preferred embodiment and berylsaddles, Raschig rings and like packing are employed in the column.Corrosion resistant structural materials are generally utilized toconstruct the desorption apparatus and materials such as stainlesssteel, nickel, glass, ceramic lined steel, are typical of types ofmaterial employed.

During desorption, the chlorinated methane containing solvent is fed tothe desorption column, preferably at or above the midpoint, and steam isintroduced to the column, preferably at the bottom. The rising steamthus countercurrently contacts the liquid solvent fed to the column. Thecolumn overhead containing steam and the chlorinated methanes withsubstantially no halogenated hydrocarbon solvent, i.e., less than 0.1percent by weight of the overhead, is passed to a condenser and phaseseparated. Part of the chlorinated methanes may be returned to thecolumn as reflux, while the major portion is removed to a still line forfractionation or to storage. Water is removed from the phase separatorand reused as steam or discarded. The recovered chlorinated methanes maybe separated by recourse to conventional distillations. Steamrequirements for a given system will depend upon the quantity of solventliquid fed to the column. Generally, enough water is supplied in theform of steam to accomplish the distillation of the chlorinated methanecontent thereof. Generally, a water feed of between 0.5 and 5.0 molesbased on the moles of chloromethane pres cut is deemed adequate. Slightexcesses are preferably used. Desorption columns may be operated atpressures ranging from atmospheric to pounds per square inch gauge.Temperatures will vary according to the pressure employed. Thus, for acolumn operated at 20 pounds per square inch gauge pressure, the top ofthe column is operated at about 34 C. with a bottom temperature of about122 C. Pressure changes in column operation will of course cause acorresponding variation in the temperatures within the column. Thestripped liquid aromatic halogenated hydrocarbon containingsubstantially no chlorinated methanes is removed from the bottom of thecolumn and recycled to the absorption zone. Recycled liquid solventcontains less than 0.20 percent chloromethanes by weight.

Gases fed in contact with the absorbing liquid are passed from anoxychlorination reactor typically through water and caustic scrubbersand, if desired, may be dried by contact with a bed of calcium chloridebefore being admitted to the absorber. While scrubbing and drying of thereactor efiiuent or gaseous chlorinated methane containing streams formsa preferred mode of operation, it is of course understood that this isnot limitative in any way since experiments have indicated that both wetand dry gases may be employed. Passing the reactor eiiiuent throughwater is preferable Where HCl recovery is desirable. If HCl is not to berecovered an alkali scrubber alone may be employed. Caustic sodasolutions are preferably employed in the alkali scrubber but recourse toother bases such as calcium hydroxide and the like is permissible. Inthe preferred method of operating this process a water scrubber isemployed to first contact the oxychlorination reaction product gases andthis is followed by a caustic soda solution scrubber to insure completeremoval of HCl from the gases. In this manner of operation, most of theHCl is recovered by the water in usable condition and small residualamounts are removed in the caustic scrubber as waste material.

The invention will be more readily understood from the followingexamples which are given as illustrative of modes of operation which maybe employed in conducting the process of this invention.

EXAMPLE I A catalyst was prepared by dissolving 441.0 grams of CuCl .2HO and 186.8 grams of KCl in 1,000 milliliters of distilled water. Onethousand milliliters of Celite pellets inch by A inch) were added to thesolution and allowed to soak for a period of 24 hours at ambienttemperatures (25 C.) The supernatant liquor (860 milliliters) wasdrained otf and the pellets dried with a Westinghouse sun lamp at atemperature of 110 C. The dried pellets had a solids loading of 33.1percent by weight of salts corresponding to 7.82 percent copper, 5.48percent potassium and 13.65 percent chloride ions by weight ofimpregnated carrier.

EXAMPLE 11 Two reactors were utilized to conduct the oxychlorination ofmethane. Reactor number 1 was a jacketed 1 /2- inch internal diametertubular reactor containing an 84- inch bed of catalyst material preparedin accordance with Example I. The second reactor was a jacketed l/z-inch internal diameter reactor containing a 108-inch bed of catalystmaterial prepared in accordance with Example I. During these runs, acontact time of 3.1 seconds was utilized with a gas ratio of feedcomponents comprising methane to HCl to air of 1 to 1.8 to 5.5 on a molebasis. A molten salt mixture was circulated in the reactor jackets andmaintained at a temperature of 370 C. The absorbing column utilized wasconstructed of a 2-inch Pyrex pipe packed with /4-inch ceramic Raschigrings to a height of 9 feet 4 inches. The liquid 1,2,4-trichlorobenzenefed to the column was fed by gravity from a head tank at ambienttemperature (25 C.) and metered through a tri-flat rotameter. The liquid1,2,4-trichlorobenzene was metered to the column and allowed topercolate down into the bottom of the column and from the bottom was ledto a reservoir connected thereto. The liquid was drained out of theabsorber bottom continuously. A depth of liquid was maintainedsufiicient to prevent the incoming gas from short circuiting into thebottom reservoir. Liquid samples were taken from the bottom as desiredthrough a stopcock provided thereon. An analysis of the vent gas fromthe absorber by mass spectrometer gave the level of chloromethanesleaving the absorber. To determine reactor productivity (chloromethanefed to the absorber), a regular product run was made in the reactorseither directly before or directly after the absorber experiment underthe same conditions of feed ratios, fiows, bath temperatures, and thelike as were employed during the absorption runs. The gaseous reactoreffluents from both reactors were fed to the column and the column Ioperated under varying conditions. The results of these experiments areshown below in Table I.

Table l ABSORPTION EXPERIMENTS 1,2,4-TRICHLOROBENZENE AT ATMOSPHERICPRESSURE Run Number 1 2 3 1 4 1 Length of run, min 60 45 3O 30 ReactorContact time, sec 3.1 3.1 1.74 1. 50 Llquid T.O.B. rate, mls./rnin 214214 361 361 Reactor output, gms./hr 144.1 150. G 338. 2 330.1 CHsCl outabsorber, gmsf 1.13 2.05 14. 55 19.42 T.O.B. out absorber, gins/hr 1. 723. 74 4. 62 Percent Reactor output absorbed 98. 9 98.6 95. 5 94. 8Llquid/gas reed ratio (molar) 9.64 7.61 5. 84 5. 03 Moles OHaCl/mcle gasin 0. 0263 0.0287 0. 0288 0.0290 Moles GH3Ol/m0le gas out 0.002 0.0010.010 0.012

1 Runs 3 and 4 were conducted on reactor gases which were not driedbefore introduction to the absorber.

EXAMPLE III The same reactor and absorber utilized in Example II wereemployed. The gas feeds and contact times employed are listed below inTable H. The reactor bath temperature was controlled at 370 C. In placeof 1,2,4- trichlorobenzene, orthodichlorobenzene was employed as theabsorption medium and the absorber was operated under a pressure of 30pounds per square inch gauge. The effluent gases from the reactors werefed to the absorption system and the results are listed below in TableII.

Table II Experiment 396 397 398 399 CH4 feed, moles/hr. 8.70 8. 70 8. 708. 70 Ch feed, moles/hm. 7. 56 7. 56 7. 56 7. 56 Air feed, m0les/hr36.00 36.00 36.00 36.00 Reactor contact time- 1. 25 1. 25 1. 25 1. 25Reactor output, gms/hr 484. 4 492.8 496. 5 496. 5 Gms/hr. to absorber331. 0 392.0 370.0 358.0 CHsOl lost thru vent, gmsJhr. 0.58 1. 24Percent CGls absorbed... 100.0 100.0 99. 8 99. 6 L/G ratio fed 9.14 5.113. 50 3. 28 Moles OHsOl/mol gas fe 0. 0396 0. 0358 0. 0298 0. 0293 MolesOHaOl/mol gas out. 0.001 0.001 Ortho. lost, gmslhr 5.20 6.00 4. 4 4. 2

As can be readily seen from an examination of the above tables, therecovery of chlorinated methanes contained in dilute quantities in aninert gas stream is efliciently accomplished utilizing liquidhalobenzenes as the absorbing liquid. While all components wereeffectively removed, very little, if any, methyl chloride was lostduring the absorption process. In addition, little or no loss ofabsorbing liquid took place. While in describing the invention and inthe specific examples hereinabove referred to, emphasis has been placedupon a counter current contact of the gas With the liquid. It is ofcourse understood that unidirectional flow of gas and liquid absorbingmedium may also be employed.

In addition to the steam stripping recovery of product hereinabovementioned, recovery of the chlorinated methane content of thehalobenzene absorption liquid may also be accomplished by recourse toordinary distillation technique. A simple heating of the absorbingliquid will readily drive off the methyl chloride content thereof andthe recovery of the methylene chloride, chloroform and carbontetrachloride fractions contained in the absorbing liquid may be readilyobtained by distillation either on a batch basis or as a continuoussystem.

While the invention has been described with reference to certainspecific examples, it is not intended to be limited thereto exceptinsofar as appears in the accompanying claims.

This application is a continuation of our copending application, SerialNo. 812,578, filed May 12, 1959, now abandoned.

We claim:

1. A method of recovering chloroform, carbon tetrachloride, methylenechloride and methyl chloride present as a gaseous mixture produced bythe catalytic reaction of methane, an oxygen containing gas and achlorinating agent selected from the group consisting of HCl, C1 andmixtures of HCl and Cl at elevated temperature, said mixture containingbelow 25 percent chlorinated methanes by volume, comprising scrubbingsaid gaseous mixture with an aqueous alkaline solution and contactingthe gaseous mixture so scrubbed with a liquid halobenzene therebyselectively absorbing the chlorinated methane content of said mixture insaid liquid halobenzene and recovering the chlorinated methanes fromsaid liquid halobenzene.

2. The method of claim 1 wherein the liquid halobenzene isortho-dichlorobenzene.

3. The method of claim 1 wherein the liquid halobenzene is1,2,4-trichlorobenzene.

4. A method of recovering chloroform, carbon tetrachloride, methylenechloride and methyl chloride present as a gaseous mixture produced bythe catalytic reaction of methane, an oxygen containing gas and achlorinating agent selected from the group consisting of HCl, C1 andmixtures of HCl and C1 at elevated temperature, said mixture containingbelow 25 percent chlorinated methanes by volume, comprising scrubbingsaid gaseous mixture in sequence with water and an aquous sodiumhydroxide solution and contacting the gaseous mixture so scrubbed with aliquid halobenzene thereby selectively absorbing the chlorinated methanecontent of the mixture in said liquid halobenezne and recovering saidchlorinated methanes from said liquid halobenzene.

5. The method of claim 4 wherein the gaseous mixture is dried after thescrubbing steps and prior to being con- 7. The method of claim 4 whereinthe liquid halobenzene is 1,2,4-trichlorobenzene.

8. A method of recovering chloroform, carbon tetrachloride, methylenechloride and methyl chloride present as a gaseous mixture produced bythe catalytic reaction of methane, an oxygen containing gas and achlorinating agent selected from the group consisting of HCl, C1 andmixtures of HC1 and C1 at elevated temperature, said mixture containingbelow 25 percent chlorinated methanes by volume, comprising scrubbingsaid gaseous mixture with water, drying the gaseous mixture so scrubbedand contacting the dried gaseous mixture with a liquid halobenzenethereby selectively absorbing the chlorinated methane content of saidmixture in said a liquid halobenzene and recovering the chlorinatedmethanes from said liquid halobenzene.

9. A method of recovering chloroform, carbon tetrachloride, methylenechloride and methyl chloride present as a gaseous mixture produced bythe catalytic reaction of methane, an oxygen containing gas and achlorinating agent selected from the group consisting of HCl, C1 andmixtures of HCl and C1 at elevated temperature comprising scrubbing saidgaseous mixture with water and an aqueous sodium hydroxide solution,drying the said gaseous mixture so scrubbed and contacting the scrubbedand dried gaseous mixtures with a liquid halobenzene thereby selectivelyabsorbing the chlorinated methane content of the gaseous mixtures insaid liquid halobenzene and recovering the chlorinated methanes fromsaid liquid halobenzene.

10. The method of claim 9 wherein the liquid halobenzene isortho-dichlorobenzene.

11. The method of claim 9 wherein the liquid halobenzene is1,2,4-trichlorobenzene.

References Cited in the file of this patent UNITED STATES PATENTS2,585,469 Johnson Feb. 12, 1952 2,750,002 Hooker et al June 12, 19562,841,243 Hooker et al. July 1, 1958 2,858,347 Hutchings Oct. 28, 19582,989,571 Eisenlohr June 20, 1961 FOREIGN PATENTS 615,106 Canada Feb.21, 1961

1. A METHOD OF RECOVERING CHLOROFORM, CARBON TETRACHLORIDE, METHYLENECHLORIDE AND METHYL CHLORIDE PRESENT AS A GASEOUS MIXTURE PRODUCED BYTHE CATALYTIC REACTION OF METHANE, AN OXYGEN CONTAINING GAS AND ACHLORINATING AGENT SELECTED FROM THE GROUP CONSISTING OF HCL, CL2 ANDMIXTURES OF HCL AND CL2 AT ELEVATED TEMPERATURE, SAID MIXTURE CONTAININGBELOW 25 PERCENT CHLORINATED METHANES BY VOLUME, COMPRISING SCRUBBINGSAID G ASEOUS MIXTURE WITH AN AQUEOUS ALKALINE SOLUTION AND CONTACTINGTHE GASEOUS MIXTURE SO SCRUBBED WITH A LIQUID HALOBENZENE THEREBYSELECTIVELY ABSORBING THE CHLORINATED METHANE CONTENT OF SAID MIXTURE INSAID LIQUID HALOBENZENE AND RECOVERING THE CHLORINATED METHANES FROMSAID LIQUID HALOBENZENE.